1. Field of the Invention
The present invention relates to apparatus for monitoring an Electrical Submersible Pump and a method of monitoring an Electrical Submersible Pump (ESP). More particularly, the present invention relates to apparatus and methods to determine a direction of rotation of a motor and/or a pump of an ESP.
2. Description of the Related Art
Electrical Submersible Pumps typically include an electric motor which drives a centrifugal pump. The electric motor and associated centrifugal pump are located in a subsurface well and the centrifugal pump enables or improves the flow of fluid from the well to the surface. The motor section of the Electrical Submersible Pump is powered by a cable which runs from a surface power source down the well to the motor section of the Electrical Submersible Pump.
It is known more generally to monitor electric motors and machinery driven by electric motors (such as centrifugal pumps) using a translational vibration sensor or accelerometer. A translational vibration sensor or accelerometer measures the translational acceleration in one or more of three orthogonal axes which are commonly referred to as the x, y and z directions. Information from the translational vibration sensor or accelerometer can be analysed to provide advance warning of potential failure of a component of the motor or machinery such as bearing failure. The information may also be used to schedule maintenance of the motor or machinery thereby preventing emergency maintenance after an unscheduled system failure.
If the motor or machinery is located in a readily accessible location then data may be gathered from the translational vibration sensor or accelerometer at a relatively rapid sample rate. The data may be stored and subsequently analysed by a computer. The high sample rate data may be converted from time-series data to frequency-series data using Fast Fourier Transform techniques thereby improving diagnostics.
However, other forms of rotating machinery such as Electrical Submersible Pumps may be located in a remote location which is relatively inaccessible. It is particularly problematic to attempt to obtain high sample rate data from a translational vibration sensor or accelerometer located in an Electrical Submersible Pump because of bandwidth limitations between the subsurface location where the Electrical Submersible Pump is located and the data acquisition system which is located at the surface.
It is known to use a translational vibration sensor or accelerometer to monitor an Electrical Submersible Pump located in an oilwell. An ESP gauge is known, for example, which monitors translational vibration (i.e. vibration from side to side). However, the ESP gauge only gives a limited amount of information about the status of the Electrical Submersible Pump. It is recognised that there is a high cost of lost production in the event that the Electrical Submersible Pump fails. The known ESP gauge communicates with the surface using the same power cable that is used to power the motor section of the Electrical Submersible Pump from the surface. The use of a single cable to provide both electrical power to the Electrical Submersible Pump from the surface and also to provide a communications route from the ESP gauge to the surface saves a considerable amount of cost which would otherwise be involved in running an extra cable into the well. However, a significant disadvantage of using a single cable to provide both electrical power and a communications route is that the bandwidth available to the ESP gauge is severely limited. As a result, the ESP gauge is restricted to sending a translational vibration reading to the surface approximately once every minute. The reading may be an average reading or a peak-to-peak reading.
The motor of a typical conventional oilfield Electrical Submersible Pump comprises a 3-phase motor driven from the surface via a 3-phase power cable. The direction of rotation of the Electrical Submersible Pump will be determined by the wiring of the 3-phase power cables which run from the surface downhole. If any two phases of a power cable is inadvertently swapped at any point between the surface and the Electrical Submersible Pump then the motor and associated pump will rotate in the opposite direction to that intended. As will be understood by those skilled in the art, the direction of rotation of an Electrical Submersible Pump is particularly important since the pump section of an Electrical Submersible Pump is only efficient when the pump is rotating in its designed or intended direction of rotation. Although an Electrical Submersible Pump will still pump fluid to a limited extent if the pump is rotated in the wrong direction, the efficiency of the pump will be severely reduced. Furthermore, if an Electrical Submersible Pump is rotated in the wrong direction for any significant period of time then the Electrical Submersible Pump is likely to overheat and the pump is likely to suffer accelerated mechanical failure.
In practical oilfield installations there is no certainty that the 3-phase power cable for an Electrical Submersible Pump has been wired correctly along the entire electrical path from the surface electrical power source to the downhole Electrical Submersible Pump motor. As a result, sometimes a newly installed Electrical Submersible Pump will inadvertently rotate in the wrong direction which can be particularly problematic if this is undetected for any significant period of time.
A known approach to this problem is to start the motor in both directions and then to compare the resulting pressure generated by the pump when the pump is rotated in both directions. It can then be determined whether or not the Electrical Submersible Pump has been correctly installed. However, this procedure is relatively time consuming. Furthermore, if the Electrical Submersible Pump has been installed correctly then the procedure imposes unnecessary and undesirable stresses upon the pump which can reduce the operating lifetime of the pump.
It is known to use a shaft rotation detector to determine the rotation direction of a motor and pump. However, placing a shaft rotation detector inside a motor or pump section significantly increases the overall mechanical complexity of the motor and pump sections and increases the risk of the pump failing.
It is desired to provide an improved apparatus including, for example, an Electrical Submersible Pump assembly including an associated pump, motor, properly configured conductors and/or umbilicals, and a processing system configured to ensure that the assembly is configured so that the motor and associated pump rotate in an intended direction.